In a wireless network, procedures may exist to provide for voice call continuity. As one example, both 3GPP and 3GPP2 define procedures for a process called Single Radio Voice Call Continuity (SRVCC). This process is generally applicable to calls in a packet-switched network, such as Voice over LTE (VoLTE) calls. For example, SRVCC may apply to VoLTE calls in which the LTE signal is no longer useable (for example, if the LTE signal becomes too weak), but where a useable signal is still available for a traditional circuit-switched network, such as CDMA. Situations like these may occur in the early days of VoLTE service rollout, when LTE coverage may not be as complete as the legacy circuit-switched network, and users may move from areas of good LTE coverage to areas of poor, or no, coverage while engaged in a phone call.
In order to avoid a dropped call, the SRVCC process is meant to hand the voice path over from the packet-switched network to the circuit-switched network while the call is in progress. Since this involves the handset re-tuning its single radio from one network technology to a different one, it results in a temporary interruption in the voice path. Minimizing this interruption is desirable, not only for the success of the handover process, but also to user satisfaction with the voice call continuity (VCC) service. In existing solutions, the processes used to handover the call may be inefficient.
One existing solution for handing over a call from a packet-switched network (such as, for example, an LTE network) to a circuit-switched network (such as, for example, a CDMA network) involves the use of a provisioned number in a wireless device. For example, the number may be a Voice Call Continuity Directory Number (VDN) in the 3GPP2 standards, or a Session Transfer Number for Single Radio (STN-SR) in the 3GPP standard). According to an existing solution, the handover process may be initiated by the packet-switched network when it detects the appropriate conditions. The packet-switched network instructs the handset, while still engaged in a call, to send a message towards the circuit-switched network to originate a second call. The call is placed to either the VDN or STN-SR. In the existing solution, the VDN or STN-SR is a static value, provisioned by the wireless device's home service provider. In such circumstances, the VDN or STN-SR represents a destination in the wireless device's home network provider's network. This results in the switching of the bearer (voice) path of the call occurring in the home network, even when the wireless device is roaming on other networks. Routing the voice path back to the wireless device's home network, regardless of where the other end point is, can result in several undesirable impacts. For example, switching of the bearer (voice) path in the home network may cause increased delays in the circuit-switched call setup process. As another example, it may result in delay due to SIP/SDP signaling updates for the packet-switched leg of the call that may need to be routed all the way to another wireless device, which may also be roaming.